what is sea floor spreading and why does the magnetic pole help us to understand this process??thank you :))
The Mid Oceanic Ridges are thin parts of Oceanic crust where under sea Basaltic Volcanoes erupt along fissures and push the oceanic crust outwards causing sea floor spreading. This lava is called Mid Oceanic Ridge Basalt (MORB) and happens along fissures in all ocean floors. The MORB is rich in magnetic crystals. These magnetic crystals align themselves along the North South magnitic polar axis and solidify into Basalt rock shortly after eruption freezing the magnetic crystals in place. An oriented piece of this rock can be used to know the direction of North and South Pole at its time of eruption. As the magnetic pole changes, the new MORB again records the new orientation. As this volcanism is a continuous process, a continuous sampling outward from Mid oceanic ridge gives a complete log of the magnetic variations called 'polar wanderings' This tells us that the location of magnetic poles at the time of eruption. This evidence suggests that magnetic north pole was earlier in the Hudson Bay and before that in Siberia. Another related fact here is that, as the sea floor spreads along the Mid Oceanic Ridges, it subducts (goes inside the mantle) along the ocean's edges in areas called 'trenches' and melts again. This happens along the contact of the Oneans and Continents. This whole process is called 'convection current'. In the Atlantic, this whole cycle takes about 225 Million Years. So we do not have any magnetic reversal records of earlier periods. And the oldest rock on the seafloor in 225 My old. Wheras we can find rocks upto over 3.2 Billion years old on the continents.
Sea floor spreading is the tectonic plate-related condition found when two plates diverge(i.e. move away from each other) . Upwelling magma fills in the fissure left in the gap. As more spread occurs, more magma rises to fill both sides of the fissure. More sea floor is formed. The magnetic domains of iron atoms in magnetite in basalt, orient to the positive magnetic pole ( North Presently)and those orientations are fixed/locked when the magnetite/iron cools below the Curie point regardless of future pole changes. When mapping the sea floor, Navy researchers found that these magnetic domains would lie in one direction then switch to the opposite pole. They also found the these bands were the same for bands equally distant to the ocean mid oceanic ridge on the opposite side. This pattern repeated may times each time resulting in an identical orientation equally distant on the opposite side of the mid-oceanic ridge. (repeated for emphasis) As the mid-oceanic ridge propagation /sea floor spreading is a conveyor belt of continuous basalt production. This alternating band of magnetic orientation could only come about it the magnetic poles were swapping orientation on a recurring basis in intervals of hundreds of thousands of years. Ergo seafloor spreading and magnetic pole orientation prove each others existence You are most welcome!
